U.S. patent application number 14/032945 was filed with the patent office on 2015-03-26 for system and method for image receiving surface treatment in an indirect inkjet printer.
The applicant listed for this patent is Xerox Corporation. Invention is credited to Chu-Heng Liu.
Application Number | 20150085037 14/032945 |
Document ID | / |
Family ID | 52623826 |
Filed Date | 2015-03-26 |
United States Patent
Application |
20150085037 |
Kind Code |
A1 |
Liu; Chu-Heng |
March 26, 2015 |
System and Method for Image Receiving Surface Treatment in an
Indirect Inkjet Printer
Abstract
An inkjet printer applies a layer of a hydrophilic composition,
which includes a liquid carrier and an absorption agent, to an
image receiving surface of an indirect image receiving member. A
dryer in the printer removes a portion of the liquid carrier from
the layer of hydrophilic composition to form a dried layer of an
absorption agent on the image receiving surface and an aqueous ink
image is formed on the dried layer. The aqueous ink image and at
least a portion of the dried layer are transferred to a surface of
a print medium as the aqueous ink image and print medium move
through a transfix nip formed between the indirect image receiving
member and a transfix member.
Inventors: |
Liu; Chu-Heng; (Penfield,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Xerox Corporation |
Norwalk |
CT |
US |
|
|
Family ID: |
52623826 |
Appl. No.: |
14/032945 |
Filed: |
September 20, 2013 |
Current U.S.
Class: |
347/102 |
Current CPC
Class: |
B41J 11/0015 20130101;
B41J 2/0057 20130101; B41J 11/002 20130101 |
Class at
Publication: |
347/102 |
International
Class: |
B41J 11/00 20060101
B41J011/00 |
Claims
1. An inkjet printer comprising: an indirect image receiving member
having an image receiving surface configured to move in a process
direction in the inkjet printer; a surface maintenance unit
configured to apply a layer of a hydrophilic composition comprising
a liquid carrier and an absorption agent to the image receiving
surface; a dryer positioned and configured to remove at least a
portion of the liquid carrier from the layer of hydrophilic
composition after the surface maintenance unit has applied the
hydrophilic composition to the image receiving surface to form a
dried layer of the absorption agent; a plurality of inkjets
configured to eject aqueous ink onto the dried layer to form an
aqueous ink image on the image receiving surface; and a transfix
member that engages the image receiving member to form a transfix
nip, the transfix member being configured to apply pressure to a
print medium moving through the transfix nip as the aqueous ink
image on the dried layer moves through the transfix nip to transfix
the aqueous ink image and the region of the dried layer that
receives the aqueous ink to a surface of the print medium.
2. The inkjet printer of claim 1 wherein the solvent is water.
3. The inkjet printer of claim 1 further comprising: a cleaning
unit positioned and configured to remove another region of the
dried layer from the image receiving surface that is not
transferred to the print medium prior to the surface maintenance
unit applying the hydrophilic composition to the image receiving
surface.
4. The printer of claim 1 further comprising: another dryer
positioned and configured to remove a portion of liquid solvent
from the aqueous ink image formed on the dried layer.
5. The printer of claim 1, the surface maintenance unit further
comprising: a reservoir containing the hydrophilic composition; and
a roller partially submerged in the reservoir and engaging the
image receiving surface, the roller being configured to rotate in
response to the movement of the image receiving member in the
process direction to draw the hydrophilic composition from the
reservoir and form the layer of the hydrophilic composition on the
image receiving surface.
6. The printer of claim 1, the surface maintenance unit being
configured to form the layer of the hydrophilic composition with a
thickness between 1 .mu.m and 10 .mu.m.
7. The printer of claim 1, the dryer being configured to remove the
portion of the liquid carrier from the layer of hydrophilic
composition to form the dried layer with a thickness of the
absorption agent between 0.1 .mu.m and 1 .mu.m.
8. The printer of claim 1 further comprising: a heater configured
to heat a temperature of the image receiving surface to a range of
50.degree. C. to 70.degree. C.
9. The printer of claim 1, the plurality of inkjets further
comprising: a first plurality of inkjets configured to eject
aqueous ink of a first color onto the dried layer; a second
plurality of inkjets configured to eject aqueous ink of a second
color onto the dried layer after the first plurality of inkjets
eject the aqueous ink of the first color.
10. The printer of claim 9 wherein the first plurality of inkjets
are configured to eject black aqueous ink.
11. The printer of claim 9 further comprising: a first dryer
positioned and configured to remove a portion of liquid solvent
from the aqueous ink of the first color formed on the dried layer
before the second plurality of inkjets eject aqueous ink of the
second color onto the dried layer; and a second dryer positioned
and configured to remove a portion of liquid solvent from the
aqueous ink of the first color and the aqueous ink of the second
color formed on the dried layer after the second plurality of
inkjets has ejected the aqueous ink of the second color onto the
dried layer.
12. The printer of claim 1, the absorption agent in the dried layer
further comprising: a material that swells in response to
absorption of the liquid solvent from the aqueous ink.
13. The printer of claim 11 wherein the absorption agent in the
dried layer is substantially impermeable to colorant in the aqueous
ink.
14. The printer of claim 1 wherein another region of the dried
layer of absorption agent in the dried layer that does not absorb
liquid solvent from the aqueous ink drops has a higher level of
adhesion to the image receiving surface than to the print medium to
enable separation of the print medium from the image receiving
surface after the print medium moves through the transfix nip.
15. The printer of claim 1, wherein the dried layer is configured
to enable a portion of a liquid solvent in the aqueous ink to
permeate a region of the dried layer that receives the aqueous ink
to reduce a level of adhesion between the region of the dried layer
and the image receiving surface
16. A method of operating an inkjet printer comprising: moving an
image receiving surface of an indirect image receiving member in a
process direction through the inkjet printer past a surface
maintenance unit, a dryer, a plurality of inkjets, and a transfix
nip; applying a layer of hydrophilic composition comprising a
liquid carrier and an absorption agent to the image receiving
surface with the surface maintenance unit; drying the layer of
hydrophilic composition with the dryer to remove at least a portion
of the liquid carrier from the layer of the hydrophilic composition
to form a dried layer of the absorption agent on the image
receiving surface; ejecting ink drops of an aqueous ink with the
plurality of inkjets to form an aqueous ink image on the dried
layer; and applying pressure with a transfix member to the image
receiving surface of the indirect image receiving member to
transfix the aqueous ink image and the region of the dried layer
that receives the aqueous ink to a surface of a print medium moving
through the transfix nip between the transfix member and the
indirect image receiving member.
17. The method of claim 16 wherein the liquid solvent is water.
18. The method of claim 16 further comprising: removing a another
region of the absorption agent in the dried layer that does not
transfer to the print medium from the image receiving surface with
a cleaning unit that engages the image receiving member after the
aqueous ink image and at least a portion of the dried layer are
transfixed to the print medium.
19. The method of claim 16 further comprising: moving the image
receiving surface in the process direction past another dryer
located between the plurality of inkjets and the transfix nip; and
drying the aqueous ink image with the other dryer to remove a
portion of liquid solvent from the aqueous ink image formed on the
layer of the absorption agent.
20. The method of claim 16 further comprising: applying the layer
of the hydrophilic composition to the image receiving surface with
a roller in the surface maintenance unit that rotates in response
to the movement of the image receiving surface and draws the
hydrophilic composition from a reservoir to form the layer of
hydrophilic composition on the image receiving surface.
20. The method of claim 20 wherein the surface maintenance unit
forms the layer of the hydrophilic composition with a thickness
between 1 .mu.m and 10 .mu.m.
22. The method of claim 16 wherein the dryer removes the portion of
the liquid carrier from the layer of hydrophilic composition to
form the dried layer with a thickness of between 0.1 .mu.m and 1
.mu.m.
23. The method of claim 16 further comprising: heating the image
receiving surface to a temperature in a range of 50.degree. C. to
70.degree. C.
24. The method of claim 16, the ejection of the ink drops further
comprising: ejecting ink drops of a first color onto the dried
layer from a first portion of the plurality of inkjets; moving the
image receiving surface with the ink drops of the first color past
a first dryer to remove a portion of liquid solvent from the
aqueous ink of the first color formed on the dried layer; ejecting
ink drops of a second color onto the dried layer from a second
portion of the plurality of inkjets after the image receiving
surface moves past the first dryer; and moving the image receiving
surface with the ink drops of the first color and the ink drops of
the second color past a second dryer to remove a portion of liquid
solvent from the aqueous ink of the first color and the aqueous ink
of the second color formed on the dried layer.
25. The method of claim 16 further comprising: retaining another
region of the dried layer of the absorption agent that does not
receive the aqueous ink drops on the image receiving surface having
a low adhesion to the print medium to enable separation of the
print medium from the image receiving surface after the print
medium moves through the transfix nip.
26. The method of claim 16, wherein the step of ejecting ink drops
is adapted to enable a portion of a liquid solvent in the aqueous
ink to permeate a region of the dried layer that receives the
aqueous ink to reduce a level of adhesion between the region of the
dried layer and the image receiving surface
Description
CROSS-REFERENCE
[0001] This application cross-references the following co-pending
U.S. patent applications, all of which were filed on Sep. 20, 2013,
and the contents and disclosure of which are incorporated herein by
reference:
[0002] Ser. No. 14/______, entitled "IMPROVED COATING FOR AQUEOUS
INKJET TRANSFER", Docket No. 1776-0599, filed on Sep. 20, 2013;
[0003] Ser. No. 14/______, entitled "IMPROVED COATING FOR AQUEOUS
INKJET TRANSFER", Docket No. 1776-0604, filed on Sep. 20, 2013;
and
[0004] Ser. No. 14/______, entitled "IMPROVED COATING FOR AQUEOUS
INKJET TRANSFER", Docket No. 1776-0607, filed on Sep. 20, 2013.
TECHNICAL FIELD
[0005] This disclosure relates generally to aqueous indirect inkjet
printers, and, in particular, to surface preparation for aqueous
ink inkjet printing.
BACKGROUND
[0006] In general, inkjet printing machines or printers include at
least one printhead that ejects drops or jets of liquid ink onto a
recording or image forming surface. An aqueous inkjet printer
employs water-based or solvent-based inks in which pigments or
other colorants are suspended or in solution. Once the aqueous ink
is ejected onto an image receiving surface by a printhead, the
water or solvent is evaporated to stabilize the ink image on the
image receiving surface. When aqueous ink is ejected directly onto
media, the aqueous ink tends to soak into the media when it is
porous, such as paper, and change the physical properties of the
media. Because the spread of the ink droplets striking the media is
a function of the media surface properties and porosity, the print
quality is inconsistent. To address this issue, indirect printers
have been developed that eject ink onto a blanket mounted to a drum
or endless belt. The ink is dried on the blanket and then
transferred to media. Such a printer avoids the changes in image
quality, drop spread, and media properties that occur in response
to media contact with the water or solvents in aqueous ink.
Indirect printers also reduce the effect of variations in other
media properties that arise from the use of widely disparate types
of paper and films used to hold the final ink images.
[0007] In aqueous ink indirect printing, an aqueous ink is jetted
on to an intermediate imaging surface, typically called a blanket,
and the ink is partially dried on the blanket prior to transfixing
the image to a media substrate, such as a sheet of paper. To ensure
excellent print quality the ink drops jetted onto the blanket must
spread and not coalesce prior to drying. Otherwise, the ink images
appear grainy and have deletions. The lack of spreading can also
cause missing or failed inkjets in the printheads to produce
streaks in the ink image. Spreading of aqueous ink is facilitated
by materials having a high energy surface. In order to facilitate
transfer of the ink image from the blanket to the media substrate,
however, a blanket having a surface with a relatively low surface
energy is preferred. These diametrically opposed and competing
properties for a blanket surface make selections of materials for
blankets difficult. Reducing ink drop surface tension helps, but
the spread is still generally inadequate for appropriate image
quality. Offline oxygen plasma treatments of blanket materials that
increase the surface energy of the blanket have been tried and
shown to be effective. The benefit of such offline treatment may be
short lived due to surface contamination, wear, and aging over
time.
[0008] One challenge confronting indirect aqueous inkjet printing
processes relates to the spread of ink drops during the printing
process. Indirect image receiving members are formed from low
surface energy materials that promote the transfer of ink from the
surface of the indirect image receiving member to the print medium
that receives the final printed image. Low surface energy
materials, however, also tend to promote the "beading" of
individual ink drops on the image receiving surface. Since a
printer partially dries the aqueous ink drops prior to transferring
the ink drops to the print medium, the aqueous ink does not have an
opportunity to spread during the printing process. The resulting
printed image may appear to be grainy and solid lines or solid
printed regions are reproduced as a series of dots instead of
continuous features in the final printed image. Consequently,
improvements to indirect inkjet printers that improve the spreading
characteristics of aqueous ink drops during an indirect printing
process would be beneficial.
SUMMARY
[0009] In one embodiment, an indirect inkjet printer forms printed
images using a hydrophilic composition and aqueous ink. The printer
includes an indirect image receiving member having an image
receiving surface configured to move in a process direction in the
inkjet printer, a surface maintenance unit configured to apply a
layer of a hydrophilic composition comprising a liquid carrier and
an absorption agent to the image receiving surface, a dryer
positioned and configured to remove at least a portion of the
liquid carrier from the layer of hydrophilic composition after the
surface maintenance unit has applied the hydrophilic composition to
the image receiving surface to form a dried layer of the absorption
agent, a plurality of inkjets configured to eject aqueous ink onto
the dried layer to form an aqueous ink image on the image receiving
surface, and a transfix member that engages the image receiving
member to form a transfix nip, the transfix member being configured
to apply pressure to a print medium moving through the transfix nip
as the aqueous ink image on the dried layer moves through the
transfix nip to transfix the aqueous ink image and at least a
portion of the dried layer to a surface of the print medium.
[0010] In another embodiment, a method for operating an indirect
inkjet printer using aqueous inks and a hydrophilic composition has
been developed. moving an image receiving surface of an indirect
image receiving member in a process direction through the inkjet
printer past a surface maintenance unit, a dryer, a plurality of
inkjets, and a transfix nip, applying a layer of hydrophilic
composition comprising a liquid carrier and an absorption agent to
the image receiving surface with the surface maintenance unit,
drying the layer of hydrophilic composition with the dryer to
remove at least a portion of the liquid carrier from the layer of
the hydrophilic composition to form a dried layer of the absorption
agent on the image receiving surface, ejecting ink drops of an
aqueous ink with the plurality of inkjets to form an aqueous ink
image on the dried layer, and applying pressure with a transfix
member to the image receiving surface of the indirect image
receiving member to transfix the aqueous ink image and at least a
portion of the dried layer to a surface of a print medium moving
through the transfix nip between the transfix member and the
indirect image receiving member.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a schematic drawing of an aqueous indirect inkjet
printer that prints sheet media.
[0012] FIG. 2 is a schematic drawing of an aqueous indirect inkjet
printer that prints a continuous web.
[0013] FIG. 3 is a schematic diagram of an inkjet printer that
includes an endless belt indirect image receiving member.
[0014] FIG. 4 is a schematic drawing of a surface maintenance unit
that applies a hydrophilic composition to a surface of an indirect
image receiving member in an inkjet printer.
[0015] FIG. 5A is a side view of a hydrophilic composition that is
formed on the surface of an indirect image receiving member in an
inkjet printer.
[0016] FIG. 5B is a side view of dried hydrophilic composition on
the surface of the indirect image receiving member after a dryer
removes a portion of a liquid carrier in the hydrophilic
composition.
[0017] FIG. 5C is a side view of a portion of an aqueous ink image
that is formed on the dried hydrophilic composition on the surface
of the indirect image receiving member.
[0018] FIG. 5D is a side view of a portion of the aqueous ink image
that is formed on the dried hydrophilic composition after a dryer
in the printer removes a portion of the water in the aqueous
ink.
[0019] FIG. 5E is a side view of a print medium that receives the
aqueous ink image and a portion of the dried layer of the
hydrophilic composition after a transfix operation in the inkjet
printer.
[0020] FIG. 6A is a side view of an image receiving surface that is
covered with a dried layer of absorption agent during a multi-color
printing process.
[0021] FIG. 6B is a side view of the image receiving surface of
FIG. 6A after a partial drying process for a multi-colored ink
image that is formed on the dried layer.
[0022] FIG. 6C is a side view of a print medium after transfer of
the multi-colored printed image to the print medium.
[0023] FIG. 7 is a block diagram of a process for printed images in
an indirect inkjet printer that uses aqueous inks
[0024] FIG. 8 is an illustration of ink drops that are formed on
low-surface energy image receiving surfaces and ink drops that are
formed on a layer of a hydrophilic composition that is formed on an
indirect image receiving surface.
DETAILED DESCRIPTION
[0025] For a general understanding of the present embodiments,
reference is made to the drawings. In the drawings, like reference
numerals have been used throughout to designate like elements. As
used herein, the terms "printer," "printing device," or "imaging
device" generally refer to a device that produces an image on print
media with aqueous ink and may encompass any such apparatus, such
as a digital copier, bookmaking machine, facsimile machine,
multi-function machine, or the like, which generates printed images
for any purpose. Image data generally include information in
electronic form which are rendered and used to operate the inkjet
ejectors to form an ink image on the print media. These data can
include text, graphics, pictures, and the like. The operation of
producing images with colorants on print media, for example,
graphics, text, photographs, and the like, is generally referred to
herein as printing or marking. Aqueous inkjet printers use inks
that have a high percentage of water relative to the amount of
colorant and/or solvent in the ink.
[0026] The term "printhead" as used herein refers to a component in
the printer that is configured with inkjet ejectors to eject ink
drops onto an image receiving surface. A typical printhead includes
a plurality of inkjet ejectors that eject ink drops of one or more
ink colors onto the image receiving surface in response to firing
signals that operate actuators in the inkjet ejectors. The inkjets
are arranged in an array of one or more rows and columns. In some
embodiments, the inkjets are arranged in staggered diagonal rows
across a face of the printhead. Various printer embodiments include
one or more printheads that form ink images on an image receiving
surface. Some printer embodiments include a plurality of printheads
arranged in a print zone. An image receiving surface, such as an
intermediate imaging surface, moves past the printheads in a
process direction through the print zone. The inkjets in the
printheads eject ink drops in rows in a cross-process direction,
which is perpendicular to the process direction across the image
receiving surface. As used in this document, the term "aqueous ink"
includes liquid inks in which colorant is in a solution, suspension
or dispersion with a liquid solvent that includes water and/or one
or more liquid solvents. The terms "liquid solvent" or more simply
"solvent" are used broadly to include compounds that may dissolve
colorants into a solution, or that may be a liquid that holds
particles of colorant in a suspension or dispersion without
dissolving the colorant.
[0027] As used herein, the term "hydrophilic" refers to any
composition or compound that attracts water molecules or other
solvents used in aqueous ink. As used herein, a reference to a
hydrophilic composition refers to a liquid carrier that carries a
hydrophilic absorption agent. Examples of liquid carriers include,
but are not limited to, a liquid, such as water or alcohol, that
carries a dispersion, suspension, or solution of an absorption
agent. A dryer then removes at least a portion of the liquid
carrier and the remaining solid or gelatinous phase absorption
agent has a high surface energy to absorb a portion of the water in
aqueous ink drops while enabling the colorants in the aqueous ink
drops to spread over the surface of the absorption agent. As used
herein, a reference to a dried layer of the absorption agent refers
to an arrangement of a hydrophilic compound after all or a
substantial portion of the liquid carrier has been removed from the
composition through a drying process. As described in more detail
below, an indirect inkjet printer forms a layer of a hydrophilic
composition on a surface of an image receiving member using a
liquid carrier, such as water, to apply a layer of the hydrophilic
composition. The liquid carrier is used as a mechanism to convey an
absorption agent in the liquid carrier to an image receiving
surface to form a uniform layer of the hydrophilic composition on
the image receiving surface.
[0028] As used herein, the term "absorption agent" refers to a
material that is part of the hydrophilic composition, that has
hydrophilic properties, and that is substantially insoluble to
water and other solvents in aqueous ink during a printing process
after the printer dries the absorption agent into a dried layer or
"skin" that covers the image receiving surface. The printer dries
the hydrophilic composition to remove all or a portion of the
liquid carrier to form a dried "skin" of the absorption agent on
the image receiving surface. The dried layer of the absorption
agent has a high surface energy with respect to the ink drops that
are ejected onto the image receiving surface. The high surface
energy promotes spreading of the ink on the surface of the dried
layer, and the high surface energy holds the aqueous ink in place
on the moving image receiving member during the printing
process.
[0029] When aqueous ink drops contact the absorption agent in the
dried layer, the absorption agent absorbs a portion of the water
and other solvents in the aqueous ink drop. The absorption agent in
the portion of the dried layer that absorbs the water swells, but
remains substantially intact during the printing operation and does
not dissolve. The absorption agent in portions of the dried layer
that do not contact aqueous ink has a comparatively high adhesion
to the image receiving surface and a comparatively low adhesion to
a print medium, such as paper. The portions of the dried layer that
absorb water and solvents from the aqueous ink have a lower
adhesion to the image receiving surface, and prevent colorants and
other highly adhesive components in the ink from contacting the
image receiving surface. Thus, the absorption agent in the dried
layer promotes the spread of the ink drops to form high quality
printed images, holds the aqueous ink in position during the
printing process, promotes the transfer of the latent ink image
from the image receiving member to paper or another print medium,
and promotes the separation of the print medium from the image
receiving surface after the aqueous ink image has been transferred
to the print medium.
[0030] As is described in more detail in cross-referenced U.S.
application Ser. Nos. 14/______ (Docket No. 1776-0599) and
14/______ (Docket No. 1776-0607), the layer of the hydrophilic
composition is formed from a material, such as starch or polyvinyl
acetate, which is dispersed, suspended, or dissolved in a liquid
carrier such as water. The hydrophilic composition is applied to an
image receiving surface as a liquid to enable formation of a
uniform layer on the image receiving surface. The printer dries the
hydrophilic composition to remove at least a portion of the liquid
carrier from the hydrophilic composition to form a dried layer of
solid or semi-solid absorption agent.
[0031] FIG. 1 illustrates a high-speed aqueous ink image producing
machine or printer 10. As illustrated, the printer 10 is an
indirect printer that forms an ink image on a surface of a blanket
21 mounted about an intermediate rotating member 12 and then
transfers the ink image to media passing through a nip 18 formed
between the blanket 21 and the transfix roller 19. The surface 14
of the blanket 21 is referred to as the image receiving surface of
the blanket 21 and the rotating member 12 since the surface 14
receives a hydrophilic composition and the aqueous ink images that
are transfixed to print media during a printing process. A print
cycle is now described with reference to the printer 10. As used in
this document, "print cycle" refers to the operations of a printer
to prepare an imaging surface for printing, ejection of the ink
onto the prepared surface, treatment of the ink on the imaging
surface to stabilize and prepare the image for transfer to media,
and transfer of the image from the imaging surface to the
media.
[0032] The printer 10 includes a frame 11 that supports directly or
indirectly operating subsystems and components, which are described
below. The printer 10 includes an indirect image receiving member,
which is illustrated as rotating imaging drum 12 in FIG. 1, but can
also be configured as a supported endless belt. The imaging drum 12
has an outer blanket 21 mounted about the circumference of the drum
12. The blanket moves in a direction 16 as the member 12 rotates. A
transfix roller 19 rotatable in the direction 17 is loaded against
the surface of blanket 21 to form a transfix nip 18, within which
ink images formed on the surface of blanket 21 are transfixed onto
a media sheet 49. In some embodiments, a heater in the drum 12 (not
shown) or in another location of the printer heats the image
receiving surface 14 on the blanket 21 to a temperature in a range
of approximately of 50.degree. C. to 70.degree. C. The elevated
temperature promotes partial drying of the liquid carrier that is
used to deposit the hydrophilic composition and of the water in the
aqueous ink drops that are deposited on the image receiving surface
14.
[0033] The blanket is formed of a material having a relatively low
surface energy to facilitate transfer of the ink image from the
surface of the blanket 21 to the media sheet 49 in the nip 18. Such
materials include silicones, fluoro-silicones, Viton, and the like.
A surface maintenance unit (SMU) 92 removes residual ink left on
the surface of the blanket 21 after the ink images are transferred
to the media sheet 49. The low energy surface of the blanket does
not aid in the formation of good quality ink images because such
surfaces do not spread ink drops as well as high energy surfaces.
Consequently, the SMU 92 applies a coating of a hydrophilic
composition to the image receiving surface 14 on the blanket 21.
The hydrophilic composition aids in spreading aqueous ink drops on
the image receiving surface, inducing solids to precipitate out of
the liquid ink, and aiding in the release of the ink image from the
blanket. Examples of hydrophilic compositions include surfactants,
starches, and the like.
[0034] In one embodiment that is depicted in FIG. 4, the SMU 92
includes a coating applicator, such as a donor roller 404, which is
partially submerged in a reservoir 408 that holds a hydrophilic
composition in a liquid carrier. The donor roller 404 rotates in
response to the movement of the image receiving surface 14 in the
process direction. The donor roller 404 draws the liquid
hydrophilic composition from the reservoir 408 and deposits a layer
of the hydrophilic composition on the image receiving surface 14.
As described below, the hydrophilic composition is deposited as a
uniform layer with a thickness of approximately 1 .mu.m to 10
.mu.m. The SMU 92 deposits the hydrophilic composition on the image
receiving surface 14 to form a uniform distribution of the
absorption agent in the liquid carrier of the hydrophilic
composition. After a drying process, the dried layer forms a "skin"
of the absorption agent that substantially covers the image
receiving surface 14 before the printer ejects ink drops during a
print process. In some illustrative embodiments, the donor roller
404 is an anilox roller or an elastomeric roller made of a
material, such as rubber. The SMU 92 is operatively connected to a
controller 80, described in more detail below, to enable the
controller to operate the donor roller, metering blade and cleaning
blade selectively to deposit and distribute the coating material
onto the surface of the blanket and remove un-transferred ink
pixels from the surface of the blanket 21.
[0035] The printers 10 and 200 include a dryer 96 that emits heat
and optionally directs an air flow toward the hydrophilic
composition that is applied to the image receiving surface 14. The
dryer 96 facilitates the evaporation of at least a portion of the
liquid carrier from the hydrophilic composition to leave a dried
layer of absorption agent on the image receiving surface 14 before
the image receiving member passes the printhead modules 34A-34D to
receive the aqueous printed image.
[0036] The printers 10 and 200 include an optical sensor 94A, also
known as an image-on-drum ("IOD") sensor, which is configured to
detect light reflected from the blanket surface 14 and the coating
applied to the blanket surface as the member 12 rotates past the
sensor. The optical sensor 94A includes a linear array of
individual optical detectors that are arranged in the cross-process
direction across the blanket 21. The optical sensor 94A generates
digital image data corresponding to light that is reflected from
the blanket surface 14 and the coating. The optical sensor 94A
generates a series of rows of image data, which are referred to as
"scanlines," as the image receiving member 12 rotates the blanket
21 in the direction 16 past the optical sensor 94A. In one
embodiment, each optical detector in the optical sensor 94A further
comprises three sensing elements that are sensitive to wavelengths
of light corresponding to red, green, and blue (RGB) reflected
light colors. Alternatively, the optical sensor 94A includes
illumination sources that shine red, green, and blue light or, in
another embodiment, the sensor 94A has an illumination source that
shines white light onto the surface of blanket 21 and white light
detectors are used. The optical sensor 94A shines complementary
colors of light onto the image receiving surface to enable
detection of different ink colors using the photodetectors. The
image data generated by the optical sensor 94A is analyzed by the
controller 80 or other processor in the printers 10 and 200 to
identify the thickness of the coating on the blanket and the area
coverage. The thickness and coverage can be identified from either
specular or diffuse light reflection from the blanket surface
and/or coating. Other optical sensors, such as 94B, 94C, and 94D,
are similarly configured and can be located in different locations
around the blanket 21 to identify and evaluate other parameters in
the printing process, such as missing or inoperative inkjets and
ink image formation prior to image drying (94B), ink image
treatment for image transfer (94C), and the efficiency of the ink
image transfer (94D). Alternatively, some embodiments can include
an optical sensor to generate additional data that can be used for
evaluation of the image quality on the media (94E).
[0037] The printer 10 includes an airflow management system 100,
which generates and controls a flow of air through the print zone.
The airflow management system 100 includes a printhead air supply
104 and a printhead air return 108. The printhead air supply 104
and return 108 are operatively connected to the controller 80 or
some other processor in the printer 10 to enable the controller to
manage the air flowing through the print zone. This regulation of
the air flow can be through the print zone as a whole or about one
or more printhead arrays. The regulation of the air flow helps
prevent evaporated solvents and water in the ink from condensing on
the printhead and helps attenuate heat in the print zone to reduce
the likelihood that ink dries in the inkjets, which can clog the
inkjets. The airflow management system 100 can also include sensors
to detect humidity and temperature in the print zone to enable more
precise control of the temperature, flow, and humidity of the air
supply 104 and return 108 to ensure optimum conditions within the
print zone. Controller 80 or some other processor in the printer 10
can also enable control of the system 100 with reference to ink
coverage in an image area or even to time the operation of the
system 100 so air only flows through the print zone when an image
is not being printed.
[0038] The high-speed aqueous ink printer 10 also includes an
aqueous ink supply and delivery subsystem 20 that has at least one
source 22 of one color of aqueous ink. Since the illustrated
printer 10 is a multicolor image producing machine, the ink
delivery system 20 includes four (4) sources 22, 24, 26, 28,
representing four (4) different colors CYMK (cyan, yellow, magenta,
black) of aqueous inks. In the embodiment of FIG. 1, the printhead
system 30 includes a printhead support 32, which provides support
for a plurality of printhead modules, also known as print box
units, 34A through 34D. Each printhead module 34A-34D effectively
extends across the width of the blanket and ejects ink drops onto
the surface 14 of the blanket 21. A printhead module can include a
single printhead or a plurality of printheads configured in a
staggered arrangement. Each printhead module is operatively
connected to a frame (not shown) and aligned to eject the ink drops
to form an ink image on the coating on the blanket surface 14. The
printhead modules 34A-34D can include associated electronics, ink
reservoirs, and ink conduits to supply ink to the one or more
printheads. In the illustrated embodiment, conduits (not shown)
operatively connect the sources 22, 24, 26, and 28 to the printhead
modules 34A-34D to provide a supply of ink to the one or more
printheads in the modules. As is generally familiar, each of the
one or more printheads in a printhead module can eject a single
color of ink. In other embodiments, the printheads can be
configured to eject two or more colors of ink. For example,
printheads in modules 34A and 34B can eject cyan and magenta ink,
while printheads in modules 34C and 34D can eject yellow and black
ink. The printheads in the illustrated modules are arranged in two
arrays that are offset, or staggered, with respect to one another
to increase the resolution of each color separation printed by a
module. Such an arrangement enables printing at twice the
resolution of a printing system only having a single array of
printheads that eject only one color of ink. Although the printer
10 includes four printhead modules 34A-34D, each of which has two
arrays of printheads, alternative configurations include a
different number of printhead modules or arrays within a
module.
[0039] After the printed image on the blanket surface 14 exits the
print zone, the image passes under an image dryer 130. The image
dryer 130 includes a heater, such as a radiant infrared, radiant
near infrared and/or a forced hot air convection heater 134, a
dryer 136, which is illustrated as a heated air source 136, and air
returns 138A and 138B. The infrared heater 134 applies infrared
heat to the printed image on the surface 14 of the blanket 21 to
evaporate water or solvent in the ink. The heated air source 136
directs heated air over the ink to supplement the evaporation of
the water or solvent from the ink. In one embodiment, the dryer 136
is a heated air source with the same design as the dryer 96. While
the dryer 96 is positioned along the process direction to dry the
hydrophilic composition, the dryer 136 is positioned along the
process direction after the printhead modules 34A-34D to partially
dry the aqueous ink on the image receiving surface 14. The air is
then collected and evacuated by air returns 138A and 138B to reduce
the interference of the air flow with other components in the
printing area.
[0040] As further shown, the printer 10 includes a recording media
supply and handling system 40 that stores, for example, one or more
stacks of paper media sheets of various sizes. The recording media
supply and handling system 40, for example, includes sheet or
substrate supply sources 42, 44, 46, and 48. In the embodiment of
printer 10, the supply source 48 is a high capacity paper supply or
feeder for storing and supplying image receiving substrates in the
form of cut media sheets 49, for example. The recording media
supply and handling system 40 also includes a substrate handling
and transport system 50 that has a media pre-conditioner assembly
52 and a media post-conditioner assembly 54. The printer 10
includes an optional fusing device 60 to apply additional heat and
pressure to the print medium after the print medium passes through
the transfix nip 18. In the embodiment of FIG. 1, the printer 10
includes an original document feeder 70 that has a document holding
tray 72, document sheet feeding and retrieval devices 74, and a
document exposure and scanning system 76.
[0041] Operation and control of the various subsystems, components
and functions of the machine or printer 10 are performed with the
aid of a controller or electronic subsystem (ESS) 80. The ESS or
controller 80 is operably connected to the image receiving member
12, the printhead modules 34A-34D (and thus the printheads), the
substrate supply and handling system 40, the substrate handling and
transport system 50, and, in some embodiments, the one or more
optical sensors 94A-94E. The ESS or controller 80, for example, is
a self-contained, dedicated mini-computer having a central
processor unit (CPU) 82 with electronic storage 84, and a display
or user interface (UI) 86. The ESS or controller 80, for example,
includes a sensor input and control circuit 88 as well as a pixel
placement and control circuit 89. In addition, the CPU 82 reads,
captures, prepares and manages the image data flow between image
input sources, such as the scanning system 76, or an online or a
work station connection 90, and the printhead modules 34A-34D. As
such, the ESS or controller 80 is the main multi-tasking processor
for operating and controlling all of the other machine subsystems
and functions, including the printing process discussed below.
[0042] The controller 80 can be implemented with general or
specialized programmable processors that execute programmed
instructions. The instructions and data required to perform the
programmed functions can be stored in memory associated with the
processors or controllers. The processors, their memories, and
interface circuitry configure the controllers to perform the
operations described below. These components can be provided on a
printed circuit card or provided as a circuit in an application
specific integrated circuit (ASIC). Each of the circuits can be
implemented with a separate processor or multiple circuits can be
implemented on the same processor. Alternatively, the circuits can
be implemented with discrete components or circuits provided in
very large scale integrated (VLSI) circuits. Also, the circuits
described herein can be implemented with a combination of
processors, ASICs, discrete components, or VLSI circuits.
[0043] In operation, image data for an image to be produced are
sent to the controller 80 from either the scanning system 76 or via
the online or work station connection 90 for processing and
generation of the printhead control signals output to the printhead
modules 34A-34D. Additionally, the controller 80 determines and/or
accepts related subsystem and component controls, for example, from
operator inputs via the user interface 86, and accordingly executes
such controls. As a result, aqueous ink for appropriate colors are
delivered to the printhead modules 34A-34D. Additionally, pixel
placement control is exercised relative to the blanket surface 14
to form ink images corresponding to the image data, and the media,
which can be in the form of media sheets 49, are supplied by any
one of the sources 42, 44, 46, 48 and handled by recording media
transport system 50 for timed delivery to the nip 18. In the nip
18, the ink image is transferred from the blanket and coating 21 to
the media substrate within the transfix nip 18.
[0044] Although the printer 10 in FIG. 1 and the printer 200 in
FIG. 2 are described as having a blanket 21 mounted about an
intermediate rotating member 12, other configurations of an image
receiving surface can be used. For example, the intermediate
rotating member can have a surface integrated into its
circumference that enables an aqueous ink image to be formed on the
surface. Alternatively, a blanket is configured as an endless belt
and rotates as the member 12 is in FIG. 1 and FIG. 2 for formation
of an aqueous image. Other variations of these structures can be
configured for this purpose. As used in this document, the term
"intermediate imaging surface" includes these various
configurations.
[0045] In some printing operations, a single ink image can cover
the entire surface 14 of the blanket 21 (single pitch) or a
plurality of ink images can be deposited on the blanket 21
(multi-pitch). In a multi-pitch printing architecture, the surface
of the image receiving member can be partitioned into multiple
segments, each segment including a full page image in a document
zone (i.e., a single pitch) and inter-document zones that separate
multiple pitches formed on the blanket 21. For example, a two pitch
image receiving member includes two document zones that are
separated by two inter-document zones around the circumference of
the blanket 21. Likewise, for example, a four pitch image receiving
member includes four document zones, each corresponding to an ink
image formed on a single media sheet, during a pass or revolution
of the blanket 21.
[0046] Once an image or images have been formed on the blanket and
coating under control of the controller 80, the illustrated inkjet
printer 10 operates components within the printer to perform a
process for transferring and fixing the image or images from the
blanket surface 14 to media. In the printer 10, the controller 80
operates actuators to drive one or more of the rollers 64 in the
media transport system 50 to move the media sheet 49 in the process
direction P to a position adjacent the transfix roller 19 and then
through the transfix nip 18 between the transfix roller 19 and the
blanket 21. The transfix roller 19 applies pressure against the
back side of the recording media 49 in order to press the front
side of the recording media 49 against the blanket 21 and the image
receiving member 12. Although the transfix roller 19 can also be
heated, in the exemplary embodiment of FIG. 1, the transfix roller
19 is unheated. Instead, the pre-heater assembly 52 for the media
sheet 49 is provided in the media path leading to the nip. The
pre-conditioner assembly 52 conditions the media sheet 49 to a
predetermined temperature that aids in the transferring of the
image to the media, thus simplifying the design of the transfix
roller. The pressure produced by the transfix roller 19 on the back
side of the heated media sheet 49 facilitates the transfixing
(transfer and fusing) of the image from the image receiving member
12 onto the media sheet 49. The rotation or rolling of both the
image receiving member 12 and transfix roller 19 not only
transfixes the images onto the media sheet 49, but also assists in
transporting the media sheet 49 through the nip. The image
receiving member 12 continues to rotate to enable the printing
process to be repeated.
[0047] After the image receiving member moves through the transfix
nip 18, the image receiving surface passes a cleaning unit that
removes residual portions of the absorption agent and small amounts
of residual ink from the image receiving surface 14. In the
printers 10 and 200, the cleaning unit is embodied as a cleaning
blade 95 that engages the image receiving surface 14. The blade 95
is formed from a material that wipes the image receiving surface 14
without causing damage to the blanket 21. For example, the cleaning
blade 95 is formed from a flexible polymer material in the printers
10 and 200. As depicted below in FIG. 3, another embodiment has a
cleaning unit that includes a roller or other member that applies a
mixture of water and detergent to remove residual materials from
the image receiving surface 14 after the image receiving member
moves through the transfix nip 18. As used herein, the term
"detergent" or cleaning agent refers to any surfactant, solvent, or
other chemical compound that is suitable for removing the dried
portion of the absorption agent and any residual ink that may
remain on the image receiving surface from the image receiving
surface. One example of a suitable detergent is sodium stearate,
which is a compound commonly used in soap. Another example is IPA,
which is common solvent that is very effective to remove ink
residues from the image receiving surface.
[0048] In the embodiment shown in FIG. 2, like components are
identified with like reference numbers used in the description of
the printer in FIG. 1. One difference between the printers of FIG.
1 and FIG. 2 is the type of media used. In the embodiment of FIG.
2, a media web W is unwound from a roll of media 204 as needed and
a variety of motors, not shown, rotate one or more rollers 208 to
propel the media web W through the nip 18 so the media web W can be
wound onto a roller 212 for removal from the printer.
Alternatively, the media can be directed to other processing
stations that perform tasks such as cutting, binding, collating,
and/or stapling the media or the like. One other difference between
the printers 10 and 200 is the nip 18. In the printer 200, the
transfer roller continually remains pressed against the blanket 21
as the media web W is continuously present in the nip. In the
printer 10, the transfer roller is configured for selective
movement towards and away from the blanket 21 to enable selective
formation of the nip 18. Nip 18 is formed in the embodiment of FIG.
1 in synchronization with the arrival of media at the nip to
receive an ink image and is separated from the blanket to remove
the nip as the trailing edge of the media leaves the nip.
[0049] FIG. 3 is a simplified schematic diagram of another inkjet
printer 300 where the indirect image receive member is in the form
of an endless belt 13. The belt 13 moves in a process direction as
indicated by the arrows 316 to pass an SMU 92, dryer 96, printhead
modules 34A-34D, and ink dryers 35A-35D to receive a dried layer of
absorption agent and a latent aqueous ink image that is formed on
the dried layer. The belt 13 is formed from a low surface energy
material, such as silicone, fluorosilicone, hydrofluoroelastomers,
and hybrids and blends of silicone and hydrofluoroelastomers, and
the like. In the printer 300, the belt 13 passes between pressure
rollers 319 and 319 that form a transfix nip 38. A print medium,
such as the media sheet 330, moves through the nip 318 concurrently
with the latent ink image. The latent ink image and a portion of
the absorption agent in the dried layer transfer from the belt 13
to the print medium 330 in the transfix nip 318 to form a printed
image. A cleaning unit 395 removes residual portions of the
absorption agent in the dried layer from the belt 13 after
completion of the transfix operation. While not expressly depicted
for simplicity, the printer 300 includes additional components that
are similar to the printers 10 and 200 including, but not limited
to, a controller, optical sensors, media supplies, a media path,
ink reservoirs, and other components that are associated with the
handling of ink and print media in an inkjet printer.
[0050] FIG. 7 depicts a process 700 for operating an aqueous
indirect inkjet printer using a hydrophilic composition to form a
dried coating or "skin" layer of a dried absorption agent in the
hydrophilic composition on an image receiving surface of an
indirect image receiving member prior to ejecting liquid ink drops
onto the dried layer. In the discussion below, a reference to the
process 700 performing an action or function refers to a
controller, such as the controller 80 in the printers 10 and 200,
executing stored programmed instructions to perform the action or
function in conjunction with other components of the printer. The
process 700 is described in conjunction with the printers of FIG.
1-FIG. 3 and FIG. 5A-FIG. 5B for illustrative purposes.
[0051] Process 700 begins as the printer applies a layer of a
hydrophilic composition with a liquid carrier to the image
receiving surface of the image receiving member (block 704). In the
printers 10 and 200, the drum 12 and blanket 21 move in the process
direction along the indicated circular direction 16 during the
process 700 to receive the hydrophilic composition. In the printer
300, the endless belt 13 moves in a loop as indicated by the
process direction arrows 316. In the printers 10 and 200, the SMU
92 applies a hydrophilic composition with a liquid carrier to the
surface 14 of the imaging drum 12. In the printer 300, the SMU 92
applies the hydrophilic composition to a surface of the imaging
belt 13.
[0052] In one embodiment, the liquid carrier is water or another
liquid, such as alcohol, which partially evaporates from the image
receiving surface and leaves a dried layer of absorption agent on
the image receiving surface. In FIG. 5A, the surface of the
indirect image receiving member 504 is covered with the hydrophilic
composition 508. The SMU 92 deposits the hydrophilic composition on
the image receiving surface 14 of the blanket 21 to form a uniform
coating of the hydrophilic composition. A greater coating thickness
of the hydrophilic composition enables formation of a uniform layer
that completely covers the image receiving surface, but the
increased volume of liquid carrier in the thicker coating requires
additional drying time or larger dryers to remove the liquid
carrier to form a dried layer of the absorption agent. Thinner
coatings of the hydrophilic composition require the removal of a
smaller volume of the liquid carrier to form the dried layer, but
if the coating of hydrophilic composition is too thin, then the
coating may not fully cover the image receiving surface. In the
embodiments of FIG. 1-FIG. 3, the printers 10, 200, and 300 form
the hydrophilic composition with the liquid carrier on the image
receiving surface with a thickness of between approximately 1 .mu.m
and 10 .mu.m.
[0053] Process 700 continues as a dryer in the printer dries the
hydrophilic composition to remove at least a portion of the liquid
carrier and to form a dried layer of the absorption agent on the
image receiving surface (block 708). In the printers 10, 200, and
300 the dryer 96 applies radiant heat and optionally includes a fan
to circulate air onto the image receiving surface of the drum 12 or
belt 13. FIG. 5B depicts the dried layer of the absorption agent
512. The dryer 96 removes of a portion of the liquid carrier, which
decreases the thickness of the layer of dried layer that is formed
on the image receiving surface. In the printers 10, 200, and 300,
the thickness of the dried layer 512 is on the order of 0.1 .mu.m
to 3 .mu.m in different embodiments, and between 0.1 to 0.5 .mu.m
in the embodiments of the printers 10, 200, and 300.
[0054] The dried layer of the absorption agent 512 is also referred
to as a "skin" layer. The dried layer 512 has a uniform thickness
that covers substantially all of the portion of the image receiving
surface that receives aqueous ink during a printing process. As
described above, while the hydrophilic composition with the liquid
carrier includes a solutions, suspension, or dispersion of the
hydrophilic material in a liquid carrier, the dried layer of the
absorption agent 512 forms a continuous matrix that covers the
image receiving surface 504. The dried layer 512 has a
comparatively high level of adhesion to the image receiving surface
504, and a comparatively low level of adhesion to a print medium
that contacts the dried layer 512. As described in more detail
below, when aqueous ink drops are ejected onto portions of the
dried layer 512, a portion of the water and other solvents in the
aqueous ink permeates the dried layer 512. The portion of the dried
layer 512 that absorbs the liquid swells, but remains substantially
intact on the image receiving surface 504.
[0055] Process 700 continues as the image receiving surface with
the hydrophilic skin layer moves past one or more printheads that
eject aqueous ink drops onto the dried layer and the image
receiving surface to form a latent aqueous printed image (block
712). The printhead modules 34A-34D in the printers 10, 200, and
300 eject ink drops in the CMYK colors to form the printed image.
When the water in the aqueous ink contacts the dried layer of the
absorption agent that is formed on the image receiving surface, the
dried layer rapidly absorbs the liquid water. Thus, each ink drop
of the aqueous ink that is ejected into the image receiving surface
expands as the absorption agent in the dried layer absorbs a
portion of the water in the liquid ink drop. The absorption of
water into the dried layer 512 also promotes binding between the
aqueous ink and the absorption agent in the dried layer to "pin" or
hold the liquid ink in a single location on the image receiving
surface 504.
[0056] As depicted in FIG. 5C, the portion of the dried layer 512
that receives aqueous ink 524 absorbs water from the aqueous ink
and swells, as is depicted by the region 520. The absorption agent
in the region 520 absorbs water and other solvents in the ink and
the absorption agent swells in response to absorption of the water
and solvent. The aqueous ink 524 includes colorants such as
pigments, resins, polymers, and the like. The absorption agent 512
is substantially impermeable to the colorants in the ink 524, and
the colorants remain on the surface of the dried layer 512 where
the aqueous ink spreads. Since the dried layer 512 is typically
less than 1 .mu.m in thickness, the absorption agent in the dried
layer 520 absorbs only a portion of the water from the aqueous ink
524, while the ink 524 retains a majority of the water.
[0057] The spread of the liquid ink enables neighboring aqueous ink
drops to merge together on the image receiving surface instead of
beading into individual droplets as occurs in traditional
low-surface energy image receiving surfaces. For example, FIG. 8
depicts examples of three printed patterns. FIGS. 804A-804B are
images of aqueous ink drops that are transferred to a print medium.
FIG. 804C shows the image of direct printing of aqueous inkjet onto
a premium inkjet photo paper. The pattern 804A depicts ink drops
that are formed on a bare image receiving surface with low-surface
energy and then are transferred to ordinary paper. The low surface
energy of the image receiving surface promotes the ink drops to
"bead" or remain in the form of individual droplets instead of
merging together. The pattern 804C depicts the printed ink drops
that are jetted directly to a high-quality paper that is
specifically coated for inkjet printing. The ink drops in the
pattern 804C spread to a greater degree than the drops in the
pattern 804A, but the paper absorbs a large proportion of the
colorant in the ink quickly, which reduces the perceptible density
of the ink. In addition, to promote spreading, the ink needs to be
on top of the substrate and remain a low viscosity liquid for some
more time. The quick & complete absorption of the ink drops
limits the amount of spreading of the ink drops. As a result, the
printed pattern still includes non-continuous lines. Prior art
printers require larger amounts of ink to fill the gaps for
higher-quality printing. The printed pattern 804B is formed using
the hydrophilic skin in the printing process. As depicted in FIG.
8, the ink drops 804B spread because the absorption agent has a
high surface energy that promotes spreading of the ink drops on the
image receiving member. Furthermore, slow absorption of the
water/solvent by the skin and the limited water absorption capacity
of the skin give the ink more time to spread. Thus, the dried layer
enables printing of solid lines and patterns as depicted in the
pattern 804B using less ink than is required with prior art
printers.
[0058] Referring again to FIG. 7, the process 700 continues with a
partial drying process of the aqueous ink on the image receiving
member (block 716). The drying process removes a portion of the
water from the aqueous ink and the hydrophilic skin layer on the
image receiving surface so that the amount of water that is
transferred to a print medium in the printer does not produce
cockling or other deformations of the print medium. In the printers
10 and 200, the heated air source 136 directs heated air toward the
image receiving surface 14 to dry the printed aqueous ink image. In
some embodiments, the image receiving member and blanket are heated
to an elevated temperature to promote evaporation of liquid from
the ink and the dried layer of the absorption agent. For example,
in the printers 10 and 200, the imaging drum 12 and blanket 21 are
heated to a temperature of 50.degree. C. to 70.degree. C. to enable
partial drying of the ink and absorption agent in the dried layer
during the printing process. The printer 300 includes multiple
dryers 35A-35D that dry the latent aqueous ink images on the
surface of the belt 13 after each of the printhead modules 35A-35D
eject aqueous ink drops, respectively. As depicted in FIG. 5D, the
drying process forms a partially dried layer 528 and aqueous ink
532 that both retain a reduced amount of water compared to the
freshly printed aqueous ink image of FIG. 5C.
[0059] The drying process increases the viscosity of the aqueous
ink, which changes the consistency of the aqueous ink from a
low-viscosity liquid to a higher viscosity tacky material. In some
embodiments, the absorption agent that absorbs a portion of the
water in the aqueous ink also acts as a thickening agent that
increases the viscosity of the aqueous ink. The drying process also
reduces the thickness of the ink 532 and the portion of the
absorption agent 528 that absorbed water from the ink 532. One
common failure mode for transfer of aqueous ink images to print
media occurs when the aqueous ink image splits. That is to say,
only about half of the ink transfers to the print medium from the
indirect image receiving surface, while the remaining portion of
the ink image remains on the indirect image receiving member. The
failure of ink transfer is typically caused by the low cohesion of
ink image layer, because the ink layer has the weakest separation
force at the exit of the transfer nip when two image receiving
surface and the substrate surface are separating. To increase the
efficiency of ink transfer, the cohesion of the ink layer or
ink/skin composite layer should be significantly greater than the
adhesion between the skin and the blanket surface. As is known in
the art, the cohesion of the ink is proportional to the viscosity
of the ink and inversely proportional to a cube of the thickness of
the ink. Thus, the drying process greatly increases the
cohesiveness of the aqueous ink. The materials in the ink 532 with
the highest degree of cohesiveness include resins or polymers that
do not permeate into the underlying absorption agent 528. The
underlying layer of the absorption agent 528 separates the
partially dried ink 532 from the image receiving surface 504, and
the water content in the absorption agent 528 reduces the adhesion
between the absorption agent 528 and the image receiving surface
504. Thus, the partially dried ink 532 and absorption agent 528
enable efficient transfer of the printed ink from the image
receiving surface 504 to a print medium.
[0060] Process 700 continues as the printer transfixes the latent
aqueous ink image from the image receiving surface to a print
medium, such as a sheet of paper (block 720). In the printers 10
and 200, the image receiving surface 14 of the drum 12 engages the
transfix roller 19 to form a nip 18. A print medium, such as a
sheet of paper in the printer 10 or a continuous paper web in the
printer 200, moves through the nip between the drum 12 and the
transfix roller 19. In the printer 300, the belt 13 and a print
medium 330 pass through a nip 318 that is formed by two pressure
rollers 320 and 319. The latent ink image is transferred from the
surface of the belt 13 and transfixed to the print medium 330 in
the nip 318. The pressure in the nip transfers the latent aqueous
ink image and a portion of the dried layer to the print medium.
After passing through the transfix nip 18, the print medium carries
the printed aqueous ink image. As depicted in FIG. 5E, a print
medium 536 carries a printed aqueous ink image 532 with the
absorption agent 528 covering the ink image 532 on the surface of
the print medium 536. The absorption agent 528 provides protection
to the aqueous ink image from scratches or other physical damage
while the aqueous ink image 532 dries on the print medium 536.
[0061] As depicted in FIG. 5E, the aqueous ink and portions of the
dried layer that absorb ink separate from the image receiving
surface 504 in the transfix nip since the image receiving surface
504 has a low level of adhesion to the absorption agent 528 that is
formed under the printed ink image 532. The dry portions of the
absorption agent in the dried layer 512 have minimal adhesion to
the print medium 536, which promotes the separation of the print
medium 536 from the image receiving surface 504 after completion of
the transfix process. By contrast, prior art release agents, such
as silicone oil, promote the release of ink from an image receiving
surface, but also form an adhesive layer between the image
receiving member and the print medium, which presents difficulty in
separating the print medium from the image receiving member after
the transfix operation. As depicted in FIG. 5E, the dry portions of
the absorption agent in the dried layer 512 typically remains on
the image receiving surface 504 after completion of the transfix
operation because the absorption agent has a low level of adhesion
to the print medium.
[0062] During process 700, the printer cleans residual portions of
the absorption agent in the dried layer from the image receiving
surface after the transfixing operation (block 724). In one
embodiment, a fluid cleaning system 395 uses, for example, a
combination of water and a detergent with mechanical agitation on
the image receiving surface to remove the residual portions of the
absorption agent from the surface of the belt 13. The fluid
cleaning system 395 uses, for example, a combination of water and a
detergent to remove the residual portions of the absorption agent
from the surface of the belt 13. In the printers 10 and 200, a
cleaning blade 95, which can be used in conjunction with water,
engages the blanket 21 to remove the residual absorption agent from
the image receiving surface 14. The cleaning blade 95 is, for
example, a polymer blade that wipes residual portions of the
absorption agent from the blanket 21.
[0063] During a printing operation, process 700 returns to the
processing described above with reference to block 704 to apply the
hydrophilic composition to the image receiving surface, print
additional aqueous ink images, and transfix the aqueous ink images
to print media for additional printed pages in the print process.
The illustrative embodiments of the printers 10, 200, and 300
operate in a "single pass" mode that forms the dried layer, prints
the aqueous ink image and transfixes the aqueous ink image to a
print medium in a single rotation or circuit of the indirect image
receiving member. In alternative embodiments, an inkjet employs a
multi-pass configuration where the image receiving surface
completes two or more rotations or circuits to form the dried layer
and receive the aqueous ink image prior to transfixing the printed
image to the print medium.
[0064] In some embodiments of the process 700, the printer forms
printed images using a single layer of ink such as the ink that is
depicted in FIG. 5A-FIG. 5B. In the printers 10, 200, and 300,
however, the multiple printhead modules enable the printer to form
printed images with multiple colors of ink. In other embodiments of
the process 700, the printer forms images using multiple ink
colors. In some regions of the printed image, multiple colors of
ink may overlap in the same area on the image receiving surface.
For example, FIG. 6A provides a diagram of the image receiving
surface 504 with a dried layer of the absorption agent 612 and a
swelled portion of the absorption agent 620. FIG. 6A depicts four
printed layers of ink 624, 628, 632, and 636. In one embodiment,
the ink layers 624-636 correspond to black, cyan, magenta, and
yellow inks, respectively. The lowest layer of ink 624 is black
ink, which is formed on the dried layer 612 before the other layers
of ink, to enable the dried layer 612 to provide the highest
quality spreading and drop retention to the black ink. In other
configurations, the printer ejects different ink colors in an
alternative order to form a portion of a printed image with a
different color of ink on the absorption agent in the dried layer
being formed first. As described above, the swelled absorption
agent in the region 620 absorbs some of the water and other
solvents in the liquid inks 624-636, but since the dried layer of
the absorption agent is less than 1 .mu.m in thickness, the liquid
ink retains a majority of the water. In FIG. 6A, all four aqueous
ink colors are printed on the image receiving surface 504 and dried
layer 612 prior to the partial drying that is described in the
process 700. FIG. 6B depicts the partially dried portion of the
absorption agent 640 with layers of partially dried ink 644, 648,
652, and 656 corresponding to the black, cyan, magenta, and yellow
inks, respectively. As depicted in FIG. 6C, the printer transfers
the multi-colored partially dried ink layers 644-656 and the
underlying portion of the absorption agent 640 to a print medium
660 during the transfix process.
[0065] The multicolor printing embodiment of FIG. 6A-FIG. 6C
corresponds to an embodiment of the process 700 where a printer
forms multiple colors of ink on a single dried layer of the
absorption agent before performing the partial drying process. In
another embodiment, the printer performs partial drying of each ink
color prior to ejecting another color of ink onto a single layer of
the absorption agent that is formed on the image receiving surface.
As depicted in FIG. 3, the printer 300 includes the dryers 35A-35D
that perform partial drying after the ejection of ink from each of
the printhead modules 34A-34D, respectively. In another embodiment
of the process 700, the printer forms printed images in a
multi-pass configuration. In the multi-pass configuration, the
printer forms a single layer of the dried absorption agent, ejects
a single color of ink, partially dries the ink, transfers the image
to the print medium, and repeats the process described above for
multiple ink colors to assemble the color image on the print medium
through subsequent transfers. For example, in a CMYK printer, the
printer performs up to four passes with each pass corresponding to
the printing with one of the CMYK inks. In this process, the
printer applies a new layer of the hydrophilic composition to the
image receiving surface during each pass.
[0066] It will be appreciated that variations of the
above-disclosed apparatus and other features, and functions, or
alternatives thereof, may be desirably combined into many other
different systems or applications. Various presently unforeseen or
unanticipated alternatives, modifications, variations, or
improvements therein may be subsequently made by those skilled in
the art, which are also intended to be encompassed by the following
claims.
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